1. Field of the Invention
The present invention relates in general to the field of viewing screens. More particularly, the present invention relates to holographic high contrast viewing screens. Specifically, a preferred embodiment of the present invention relates to a liquid crystal display (LCD) wherein a holographically produced structural feature is embedded within the liquid crystal cell so as to provide a holographic high contrast viewing screen. The present invention thus relates to a holographic high contrast viewing screen of the type that can be characterized as embedded in a liquid crystal display.
2. Discussion of the Related Art
Liquid crystal displays are well-known to those skilled in the art. For example, such displays are described in E. Kaneko, Liquid Crystal TV Display, Principles and Applications of Liquid Crystal Display, D. Reidel Pub. Co., Boston, (1987), the entire disclosure of which is hereby expressly incorporated by reference into the present application for the purposes of indicating the background of the present invention and illustrating the state of the art.
Twisted nematic liquid crystals of the type hereunder consideration, sometimes called nematics, are also well-known to those skilled in the art. Conventional nematic materials typically have structures that can be represented by: ##STR1## where X, Y is Cyano-CN, Alkyl-CH.sub.3 (CH.sub.2).sub.n and/or Alkioxy-CH.sub.3 (CH.sub.2).sub.n O; A--B is Biphenyl (-) or Ester-COO--; and .phi. is phenyl, cyclohexyl or biphenyl. Such compounds are readily commercially available from commercial vendors such as Merck and BDH under the designations ZLI1646, ZLI2452, ZLI1167 and E7, E8, . . . E44, respectively. Specific examples of base nematics with chiral additives include: ##STR2##
As is well-known to those skilled in the art, the light that passes through a liquid crystal based flat panel display is typically generated by fluorescent lamps located either at the edges, or immediately behind, a backlight. These configurations are commonly found in lap-top computer screens, as well as displays in aircraft cockpits and various scientific equipment.
As is also well-known to those skilled in the art, if the light that passes through a liquid crystal display is distributed everywhere, then the display will appear less bright than if the display sends its light only to one or, perhaps, two viewers of choice. Thus, a previously recognized problem has been that, if the output from a liquid crystal display is not shaped into a viewing area, then the display will appear relatively dark.
However, the light passing through a liquid crystal based flat panel display is extremely difficult to direct towards specific viewers. Therefore, the brightness of such displays is often compromised.
Thus, what is needed is a way of shaping the light from a liquid crystal based flat panel display. Further, what is also needed is a way of shaping the light that is optically optimized for the optical characteristics of a particular liquid crystal display. Heretofore these requirements have not been fully met without incurring various disadvantages.
The disclosures of all the below-referenced prior United States patents, in their entireties are hereby expressly incorporated by reference into the present application for purposes including, but not limited to, indicating the background of the present invention and illustrating the state of the art. U.S. Pat. No. 4,309,093 discloses a method of replicating a diffusing plate. U.S. Pat. No. 4,336,978 discloses a method for optically making a diffusion plate. U.S. Pat. No. 5,365,354, discloses method of making a GRIN type diffuser based on volume holographic material.